Ice packs are a great way to keep your lunch cool, but they're a bit expensive if you're in the habit of losing them. Over on cooking blog My Kitchen Escapades they show a cheap, reusable, and easy way to make ice packs from kitchen sponges.

All you need to do is take a standard kitchen sponge, soak it in water, put it inside a ziploc bag, and freeze it. When you're done, you have an ice pack. The handy thing is that when the ice starts to melt, the sponge soaks up the water so it doesn't leak everywhere. If you're looking to upgrade your brown-bag lunch this should be a helpful trick.